The present invention relates to a pneumatic radial passenger-car tire, which is improved in the driving stability, comfortableness in riding, and high speed durability by improving the vicinities of tire beads.
With a recent trend of ever-perfecting freeway networks and upgrading performances of passenger cars, there seems no limit in the upgrading performance as well as increasing versatility required of tires.
For example, HR tires capable of traveling at speeds higher than SR tires, and VR tires capable of traveling at further higher speeds have been demanded. Furthermore, development of flat tires superior in driving stability has been demanded.
On the other hand, from the standpoint of vehicles, there is a demand for tires with flatness as usual but capable of traveling at higher speeds and superior in driving stability in consideration to tire houses.
In view of the above, tire manufactureres have heretofore tried to cope with such various demands by additionally providing reinforcing sheets made of organic fiber cords in the bead portions of a tire, which is called "bead portion reinforcing layers." Since the reinforcing sheets have been made of the same material as a conventional material constituting a carcass layer, however, reinforcement has been so insufficient that the above-mentioned demand, namely the demand for tires with flatness as usual but capable of traveling at higher speeds and superior in driving stability, could not have been met.
On the basis of a reflection that the same material as that constituting a carcass layer is unsatisfactory, there has later been proposed use of a reinforcing sheet comprising steel cords as the bead portion reinforcing layer. Although in this case the effect of such use is recognized in improvements in the high speed performance, driving stability, and the like, however, the downgrading of comfortableness in riding is intolerably serious due to the high flexural rigidity of steel cords. Thus, further improvement has been demanded.